Improved supportive care for patients with malignant disorders has contributed significantly to more effective cancer therapy. The hazards presented by leukopenia remain as the limiting factor in most current cancer therapy. Continuous flow filtration leukopheresis, developed in this laboratory, makes available large numbers of normal granulocytes and monocytes suitable for human transfusion. This makes it possible to study the role of leukocyte transfusions in the control of infection in patients with leukopenia. Assessment of the function of isolated leukocytes and of their in vivo effects is complex, and it will be approached by an integrated group of investigators involved in the study of leukocytes at the Mercy Catholic Medical Center and the University of Pennsylvania, each with established expertise in their corresponding areas of interest. Their goal will be to fully develop an effective preparation of leukocytes for the control of infection by means of leukocyte transfusions and to extend the knowledge of granulocyte and monocyte function in order to adequately assess these leukocytes both before and after their transfusion into leukopenic patients.